The PIM protein kinases which include the closely related PIM-1, -2, and -3, have been implicated in diverse biological processes such as cell survival, proliferation, and differentiation. PIM-1 is involved in a number of signaling pathways that are highly relevant to tumorigenesis [reviewed in Bachmann & Moroy, Internat. J. Biochem. Cell Biol., 37, 726-730 (2005)]. Many of these are involved in cell cycle progression and apoptosis. It has been shown that PIM-1 acts as an anti-apoptotic factor via inactivation of the pro-apoptotic factor BAD (Bcl2 associated death promoter, an apoptosis initiator). This finding suggested a direct role of PIM-1 in preventing cell death, since the inactivation of BAD can enhance Bcl-2 activity and can thereby promote cell survival [Aho et al., FEBS Letters, 571, 43-49 (2004)]. PIM-1 has also been recognized as a positive regulator of cell cycle progression. PIM-1 binds and phosphorylates Cdc25A, which leads to an increase in its phosphatase activity and promotion of G1/S transition [reviewed in Losman et al., JBC, 278, 4800-4805 (1999)]. In addition, the cyclin kinase inhibitor p21Waf which inhibits G1/S progression, was found to be inactivated by PIM-1 [Wang et al., Biochim. Biophys. Act. 1593, 45-55 (2002)]. Furthermore, by means of phosphorylation, PIM-1 inactivates C-TAK1 and activates Cdc25C which results in acceleration of G2/M transition [Bachman et al., JBC, 279, 48319-48 (2004)].
PIM-1 appears to be an essential player in hematopoietic proliferation. Kinase active PIM-1 is required for the gp130-mediated STAT3 proliferation signal [Hirano et al., Oncogene 19, 2548-2556, (2000)]. PIM-1 is overexpressed or even mutated in a number of tumors and different types of tumor cell lines and leads to genomic instability. Fedorov, et al., concluded that a Phase III compound in development for treating leukemia, LY333′531, is a selective PIM-1 inhibitor. O. Fedorov, et al., PNAS 104(51), 20523-28 (December 2007). Evidence has been published to show that PIM-1 is involved in human tumors including prostate cancer, oral cancer, and Burkitt lymphoma (Gaidano & Dalla Faver, 1993). All these findings point to an important role of PIM-1 in the initiation and progression of human cancers, including various tumors and hematopoietic cancers, thus small molecule inhibitors of PIM-1 activity are a promising therapeutic strategy.
Additionally, PIM-2 and PIM-3 have overlapping functions with PIM-1 and inhibition of more than one isoform may provide additional therapeutic benefits. However, it is sometimes preferable for inhibitors of PIM to have little or no in vivo impact through their inhibition of various other kinases, since such effects are likely to cause side effects or unpredictable results. See, e.g., O. Fedorov, et al., PNAS 104(51), 20523-28 (December 2007), discussing the effects that non-specific kinase inhibitors can produce. Accordingly, in some embodiments, the invention provides compounds that are selective inhibitors of at least one of PIM-1, PIM-2, and PIM-3, or some combination of these, while having substantially less activity on certain other human kinases, as described further herein.
The implication of a role for PIM-3 in cancer was first suggested by transcriptional profiling experiments showing that PIM3 gene transcription was upregulated in EWS/ETS-induced malignant transformation of NIH 3T3 cells. These results were extended to show that PIM-3 is selectively expressed in human and mouse hepatocellular and pancreatic carcinomas but not in normal liver or pancreatic tissues. In addition, PIM-3 mRNA and protein are constitutively expressed in multiple human pancreatic and hepatocellular cancer cell lines.
The link between PIM-3 overexpression and a functional role in promoting tumorigenesis came from RNAi studies in human pancreatic and hepatocellular cancer cell lines overexpressing PIM-3. In these studies the ablation of endogenous PIM-3 protein promoted apoptosis of these cells. The molecular mechanism by which PIM-3 suppresses apoptosis is in part carried out through the modulation of phosphorylation of the pro-apoptotic protein BAD. Similar to both PIM-1 and PIM-2 which phosphorylate BAD protein, the knockdown of PIM-3 protein by siRNA results in a decrease in BAD phosphorylation at Ser112. Thus, similar to PIM-1 and 2, PIM-3 acts a suppressor of apoptosis in cancers of endodermal origin, e.g., pancreatic and liver cancers. Moreover, as conventional therapies in pancreatic cancer have a poor clinical outcome, PIM-3 could represent a new important molecular target towards successful control of this incurable disease.
At the 2008 AACR Annual Meeting, SuperGen announced that it has identified a lead PIM kinase inhibitor, SGI-1776, that causes tumor regression in acute myelogenous leukemia (AML) xenograft models (Abstract No. 4974). In an oral presentation entitled, “A potent small molecule PIM kinase inhibitor with activity in cell lines from hematological and solid malignancies,” Dr. Steven Warner detailed how scientists used SuperGen's CLIMB™ technology to build a model that allowed for the creation of small molecule PIM kinase inhibitors. SGI-1776 was identified as a potent and selective inhibitor of the PIM kinases, inducing apoptosis and cell cycle arrest, thereby causing a reduction in phospho-BAD levels and enhancement of mTOR inhibition in vitro. Most notably, SGI-1776 induced significant tumor regression in MV-4-11 (AML) and MOLM-13 (AML) xenograft models. This demonstrates that inhibitors of PIM kinases can be used to treat leukemias.
Fedorov, et al., in PNAS vol. 104(51), 20523-28, showed that a selective inhibitor of PIM-1 kinase (Ly5333′531) suppressed cell growth and induced cell death in leukemic cells from AML patients. PIM-3 has been shown to be expressed in pancreatic cancer cells, while it is not expressed in normal pancreas cells, demonstrating that it should be a good target for pancreatic cancer. Li, et al., Cancer Res. 66(13), 6741-47 (2006).
Another kinase shown to be a useful target for certain cancers, including leukemia, is Flt3 kinase (FMS-like tyrosine kinase 3). Flt3 is prevalent in refractory AML patients, so inhibitors of Flt3 are useful to treat such patients. Smith, et al., reported an alkaloid called CEP-701 that is a potent inhibitor of Flt3 and provided clinical responses in tested subjects with minimal dose-related toxicity. Blood, vol. 103(10), 3669-76 (2004). Dual inhibitors that are active against both PIM and Flt3 may be advantageous over inhibitors of either target alone. In particular, excessive Flt3 activity is associated with refractory AML, so dual inhibitors of PIM and Flt3 such as compounds disclosed herein are useful to treat refractory AML.
In addition, Flt3 inhibitors are useful to treat inflammation. Inhibitors of Flt3 have been shown to be effective to treat airway inflammation in mice, using a murine asthma model. Edwan, et al., J. Immunologoy, 5016-23 (2004). Accordingly, the compounds of the invention, and particularly compounds of formula (II) and formula (III) are useful to treat conditions associated with excessive activity of Flt3, including inflammation such as airway inflammation and asthma.
Collectively, these results demonstrate that inhibitors of PIM kinases and Flt3 kinase are useful for treating certain types of cancers. Accordingly, the identification of compounds that specifically inhibit, regulate and/or modulate the signal transduction of PIM-1, PIM-2, PIM-3, and/or Flt3 is desirable as a means to treat or prevent disease states associated with abnormal cell proliferation, such as cancer. The invention provides compounds, compositions and methods that address this need and are useful for treating cancers.